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1997 chevy cavlier using more gas

On a 4 hr trip it would normal use a half tank of gas, however it now takes almost a full tank. What would be the cause of this?



The oil pan light comes on, it goes on and off sometimes. What does this mean?

First you need to check that oil level before you drive or even start the car.

Next ??  Lots of things could cause increased fuel usage.  If it is truly using twice as much fuel per mile then something is seriously wrong, which could be nothing more than plugs, plug wires, fuel filter air filter etc.  or it could be just poor measurements cold weather etc. 

Measuring mileage by the tank is generally a very inaccurate measurement. You need to measure miles per gallon.  Fill the tank and note the mileage.  Now drive until you need fuel again and then fill the tank and note the mileage and the amount of fuel.  Subtract the starting mileage from the final mileage and divide by the number of miles.  Doing this like three times in a row will give you accurate information.  

With the information presented, the only thing I know is a problem is the oil light.

Oil light (if red) means low oil pressure. It is either a bad sensor or mechanical problem(severe/death of engine likely).

Use miles traveled/gallons of fuel to get MPG and meaningful comparison. The fuel gauge is never linear and meaningless for MPG. It is good hopefully to tell you when tank is fuel, empty, 1/2 full that is it.

The oil pressure warning light is alerting you to low oil pressure. The pressure switch that controls the light could be bad, or there could be a problem with the oil pump or other internal engine parts.

You should have the oil pressure tested to determine the exact cause of the light. Driving with the oil pressure warning light on is not a good idea. If there is insufficient oil pressure the engine can be severely damaged in a VERY short time.

The oil pressure light is much more important right now than the gas mileage. Have this checked ASAP.

What is an “oil pan light”? Please check your owner’s manual and see what this really is. If it’s a low oil pressure light and the sensor is working correctly, then you’ve been damaging your engine by continuing to run it in this condition.

Your oil pan has a float inside that senses the oil level. Check the oil level and if it’s fine, there’s a problem with the oil level sensor. This could be a poor connection at the sensor, or the sensor itself. A common problem with GM vehicles with this sensor.

As far as the poor fuel economy, a thermostat that’s stuck open can cause this, or a faulty coolant temp sensor for the computer can cause this.

Tester

Got the car in Dec. I changed the spark plugs right away, check air filter which looks brand new and had the oil changed. Been keeping an eye on the oil level which is good.

The Oil light has not come back for 2 days now. Should I change the sensor out?

See above.

I put a new thermostat and top radiator hose on, before the poor fuel economy. Now it using antifreeze again. It wasn’t using antifreeze for a while and the level light stays on. Should I replace the overflow tank because I can’t see if the fluid is up to the mark? It has divider in it.

If monitoring the level of the overflow is important to you and it is so cloudy you can’t see the level,replace it. You could find a alternate method to check level than sight.

I put a new thermostat and top radiator hose on, before the poor fuel economy.

Are you sure you used the right thermostat and are you sure the current one is operating properly?

The thermostat I got was from Auto zone. I put it in about 3 weeks ago. I Temp is acting right like it should.

I check with auto zone, they don’t have the tank. Where can I get a new one, and how else can I check it? I can’t see another alternate way.

Well, I’ll be! It does have an oil level switch. Here is how to replace that: http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c1528003cbb3
It uses antifreeze because the level in the overflow bottle is low, after you replaced cooling system parts?! To fully fill the cooling system, you have to run the engine and bleed the air out. If you didn’t bleed the air, and top off the radiator; filling the overflow bottle may not be enough coolant to replace the air which bled, by itself, from the cooling system. Top off the radiator, directly.
If there isn’t enough coolant in the engine to cover the sensor tip of the engine coolant temperature sensor, that sensor CAN’T read correctly. Once coolant actually covers the sensor tip, it will (likely) read correctly.

Use the Dealer for the part,use a stick to check the level.

It is using coolant but not sure if it the head gasket. There is none going on the ground that I can see. I have flushed the engine out also I check the spark plugs and they look normal.